Here is a short, sweet book beyond easy categorisation. Is it biography or autobiography, social history or meditation, complex literary contrivance or gushing stream of consciousness? All of them, perhaps, with wry self-revelation added. Whatever he set out to write in 'this pot into which I am stirring almost anything that occurs to me', Kureishi has produced something fresh in form and memorable for the light it sheds.

The basic idea is simple enough. Kureishi hovers on the brink of 50, looking back as well as forward. He discovers an unpublished novel by his (dead and generally unpublished) father. It's called The Age of Adolescence and takes his upper-middle-class Poona family - lightly disguised - through the birth of India, the flight to Pakistan and the diaspora that followed. Welcome to Bromley, suburbia with the roots hacked off.

This is a voyage into, rather than around, his father, into the past and a lost world. Where's truth and where's fiction? Did Shani, fiction's wandering survivor of adolescence, really become Shannoo Kureishi, eking out a bureaucratic life at the Pakistani high commission in Knightsbridge and dreaming of immortality - either cricketing or literary - through his son? Is Shani's fictional brother, Mahmood, in fact, Hanif's glamourous uncle Omar, Pakistan's commentating and columnising answer to Christopher Martin-Jenkins?

Nothing is quite certain. But uncertainty is part of Kureishi's game plan as he weaves between paternal introspection and his own experience, a writer talking about and almost to himself. Very occasionally, this is mildly irritating.

There's a far more straightforward narrative on offer, ready to be unrolled: Shannoo Kureishi's sense of failure, especially when he compared himself to brother Omar, and how his real (much larger than fictional) family was scattered in a cultural context neither Indian nor English. How does national identity transplant itself from Poona to Lower Penge?

For Kureishi, there's more than a homage to pay. He needs to decide whether, 11 years after his father's death, he has fulfilled Shannoo's and his own hopes. So, slightly portentously, the text becomes littered with great names - Philip Roth, Kundera, Chekhov, VS Naipaul. The pendulum swings back from portent; then we're in Hastings today with Hanif with his young family and posters for Des O'Connor and Elkie Brooks. A pot into which anything may be stirred? More than that.

If a writer can simulate complete relaxation with an effortless flow, the effect can be hypnotic and revelatory. For long stretches, Kureishi achieves precisely this.

His father is both a tragic figure and the warmest influence, the patriarch from Poona washed up on a distant shore. He dies in hospital, without warning - 'There am I out on the street at five in the morning, with out him forever, and Mother saying, "I just want him to come home".' But at home, in the forgotten, unturned pages of his novels lies another, continuing life, a cross-referencing system of exploration and remembrance.

Would a harder structure of facts, dates and questions have served us better? No, for what comes here, at its easy best, roams deeper. We need the disembodied family from Pakistan, these secondary remnants of a ruling raj with their army uniforms and RAF blazers, to paint an exotic backdrop. We need Shani/Shannoo's first sex (at 15), with a prostitute who, 'knitting her fingers around his penis, tells him that "sex is where man meets his Brahma, you go into a world of higher joy", so that Hanif's own experiments and failures with higher joy have a sometimes wincing relevance. We even begin to see ourselves more unsparingly as Kureishi mixes love, awe and sadness in a delineation of family life which sits us in the Bromley parlour after supper and hears the sighs and silences.

The Kureishis, of course, are not quite as ordinary as Hanif would have us believe. They were, and are, exceptionally cultured and talented. They were people of status in the old India. That applies still in south London, Dorset, New York or wherever they come to rest. Omar writes memoirs, too. Shannoo, like Hanif, married a white Brit.

Their experience is special. But what is even more special is Hanif Kureishi's ability to write with a subtlety which makes this free-form sing. I think his father, who was pretty hooked on a loose, free-form himself, would have been proud. And that is probably the best thing any critic can say.